REIGN CHALLENGES SUPERGIRL - Supergirl (Melissa Benoist) investigates a mysterious symbol popping up all over National City, tracing its origins back to an ancient prophecy and the mark of the World Killer, Reign (Odetee Annable). Meanwhile, the tension between Lena (Katie McGrath) and Morgan Edge (guest star Adrian Pasdar) continues to build, causing James to step in and offer up some protection, and possibly igniting a spark in the process.

THE FLASH Episode Title: S04E09 "Don't Run"

KATEE SACKHOFF RETURNS AS AMUNET - Amunet (guest star Katie Sackhoff) kidnaps Caitlin (Danielle Panabaker) and puts meta-dampener handcuffs on her to keep her from turning into Killer Frost. Amunet tells Caitlin she needs her to perform a tricky medical task and if Caitlin fails, Amunet will kill her. Meanwhile, The Thinker (guest star Neil Sandilands) traps The Flash (Grant Gustin) in a speedster-proof prison. With the clock ticking, The Team doesn't have the time or resources to track both Caitlin and Barry so Iris (Candice Patton) is forced to choose who to save.

FOLLOW YOUR HEART - Rattled by recent events, the Legends dive into work which finds them investigating an Anachronism in a Viking settlement in the New World. The Legends realize that the Norsemen are worshipping an artifact as their god and are surprised by the artifact's origin. For the first time, Sara (Caity Lotz) is worried that they might need back up when Damien Darhk (Neal McDonough) shows up. Meanwhile, Jax (Franz Drameh) finds a loophole that could potentially change history, but it is a risk he is willing to take.

ARROW Episode Title: S06E09) "Irreconcilable Differences"

BLACK SIREN KIDNAPS LANCE - Quentin Lance (Paul Blackthorne) is kidnaped by Black Siren (Katie Cassidy) and Cayden James (guest star Michael Emerson), who are looking to trade Lance's life for a weapon of mass destruction. Oliver (Stephen Amell) and Team Green Arrow must figure out a way to save Lance while still keeping the city safe.